Upton would automatically become the 2nd/3rd best defender, best speed player, third/4th best offensive player on the tigers if they were to trade for him ( I'm only counting players who would be considered every day players). Upton worst full year is 2.5 WAR. Porcello barely averages above 2.5. Upton has the potential to put up a Cabrera type year according to WAR ( as evidenced by his 6.4 WAR a mere season ago). If you want to cite park as his weakness, Dave Cameron pretty much covered that (
http://www.fangraphs.com/blogs/index.php/justin-upton-is-not-a-park-effect-mirage/ ) Upton is a solid major league rf that possesses MVP potential at the tender age of 25 whose career arc coincides right alongside the core of the team ( Cabrera, verlander, fielder, Jackson, Avila, scherzer). If I need to explain any more about this man, I really can not understand your reasoning as to why you wouldn't be overjoyed to have him on the tigers? You'd rather wait for castellanos to relearn a whole new position on the possibility he MIGHT help the tigers compete for a WS in 2015? Or would you rather have the guy who can help the tigers compete for a WS in 2013, 2014, 2015, or possibly beyond? A package of castellanos and porcello could match the mariners offer, and could leave the cupboard bare for a second, but when you have three ( possibly 4) MVP contenders on your team, does it matter anymore? Ask the yankees if it matters.